Eu-doped Ca Research Articles

Dual-emission Eu-doped Ca2−xSrxPN3nitridophosphate phosphors prepared by hot isostatic press

Here, we demonstrate a series of Ca2−xSrxPN3:Eu2+nitridophosphate phosphors synthesized through a hot isostatic press with unexpected dual-emission in the red and infrared regions.

Crystal growth and scintillation properties of Eu-doped Ca(BrxI1–x)2 crystals

In this study, solid solutions of Ca(Br,I)2 were prepared to mitigate the cleavage feature of CaI2. Samples were grown using the Bridgman–Stockbarger (BS) method in a quartz ampoule. Eu2+ 4f–5d emissions were observed, peaking at 462–464 nm with a scintillation decay time of around 1000–1500 ns. Eu2%:CaBr0.5I1.5 showed the best light output of 109,000 photons/MeV, and Eu2%:CaBrI showed the best energy resolution (7.9%@662 keV) among the crystals grown. Eu2%:CaBr0.5I1.5 showed the same crystal phase as CaI2 and a strong cleavage feature. In contrast, Eu2%:CaBrI did not exhibit the cleavage feature and was more feasible for mass production as a detector material. Eu-doped CaBrI was the most promising material, not only for applications in the observation of neutrinoless double beta decay, but also other high-energy physics, gamma ray surveys, and gamma camera applications, owing to the optimization of light yield and energy resolution without cleavage.

Low-temperature solid state synthesis of Eu-doped Ca 2 SnO 4 ceramics under CO-CO 2 atmosphere

Abstract High temperature solid state is reported the most common synthesis technique for Ca2SnO4 ceramics, nevertheless it requires high thermal treatment temperature and long synthesis time. Our previous studies indicated that Ca2SnO4 was much easier to form if SnO2 and CaCO3 were roasted under CO-CO2 atmosphere at relatively low temperatures. In this study, the reaction mechanism between SnO2 and CaCO3 under 15 vol% CO/(CO+CO2) atmosphere and air atmosphere were firstly investigated by using XRD, SEM, XPS, etc. In addition, the Eu-doped Ca2SnO4 was synthesized by low-temperature solid state reaction under CO-CO2 atmosphere. The results indicated that the crystal structure and photoluminescence properties of the products were similar to those of samples synthesized under air atmosphere, whereas the synthetic temperature was reduced by more than 300 °C.

Combustion synthesis and luminescence properties of Eu-doped Ca–α-SiAlON

Investigated were the combustion synthesis of Eu-doped Ca–α-SiAlONs and their luminescence properties. Experimentally established were (a) green compositions ensuring maximal extent of conversion, (b) influence of elemental composition on phase composition and microstructure of synthesized Ca–α-SiAlONs, and (c) influence of elemental composition on the excitation and emission spectra of Ca–α-SiAlON luminophors.

Controllable Eu valence for photoluminescence tuning in apatite-typed phosphors by the cation cosubstitution effect.

By cosubstituting [Ca(2+)-P(5+)] for [La(3+)-Si(4+)] in the Eu-doped Ca(2→8)La(8→2)(SiO4)6-x(PO4)xO2 (0 ≤ x ≤ 6) system, Eu(3+) ions are controllably and gradually transformed to Eu(2+). Thus, the emission colors consecutively changed from red to blue/green light. Furthermore, excellent warm-white lights with the low correlated color temperature (CCT) range of 3500-3800 K and a high color rendering index (Ra) (88.4-93.2) have been achieved by mixing the as-prepared phosphors at different cation cosubstitution ratios.

Synthesis, structure and tunable red emissions of Ca(Al/Si)2N2(N1−xOx):Eu2+prepared by alloy-nitridation method

A series of phosphors, Eu-doped Ca(Al/Si)2N2(N1−xOx), derivatives of CaAlSiN3, were synthesized by alloy-nitridation method. We demonstrated that their emission peaks can be tuned from 650nm to 610nm by oxygen preferential substitutions of nitrogen located at one of two crystallographic sites. Two luminescent centers corresponding to two types of Eu2+-coordination modes, i.e. EuNI2NII3 and EuNI2NII2O, were identified and accounted for the emission band structures, emission band shifts with oxygen/nitrogen substitutions, and the dependence of peak position and integrated emission intensity on temperature. As a typical example, Ca(Al/Si)2N2(N0.80O0.20):0.02Eu showed intense orange–red emission peaking at 622nm and kept the feature of excellent chemical stabilities, which would have potential applications in fabricating the white light-emitting diode. The excellent luminescent properties of these materials, such as wavelength-tunable red emission and excellent chemical stabilities, make them practical for use in typical LED package.

Excellent red phosphors of double perovskite Ca 2La MO 6:Eu ( M=Sb, Nb, Ta) with distorted coordination environment

Double perovskite Ca 2LaSbO 6, successfully synthesized by solid state reaction method, was identified by Rietveld refinements to crystallize in the monoclinic space group P2 1/ n, which is isostructural to Ca 2La MO 6 ( M=Nb, Ta). Excellent red luminescence of Eu-doped Ca 2La MO 6 ( M=Sb, Nb, Ta) can be obtained and no luminescence quenching effect was observed when Eu-doping level reached 40%. For Ca 2La 0.6NbO 6:0.4Eu 3+, quantum efficiencies of 20.9% and 27.7% were reached to show high light conversion and bright red emission excited at 465 nm (blue light) and 534 nm (green light), respectively, comparable to the commercial phosphors. Through systemic investigation for the series of double perovskite compounds, the excellent red emission in Ca 2LaMO 6 is attributed to highly distorted polyhedra of EuO 8 (low tolerance factor of the pervoskite), and large bond distances of La−O (low crystal field effect of the activator).

Eu-doped Ca 8Mg(SiO 4) 4Cl 2 phosphor particles prepared by spray pyrolysis from the colloidal spray solution containing ammonium chloride

The green-emitting Ca 8Mg(SiO 4) 4Cl 2:Eu 2+ phosphor particles were prepared by spray pyrolysis from the colloidal spray solution that contained fumed silica and ammonium chloride. The ammonium chloride was used as the source of chlorine and the flux material. The ratios of the calcium and chlorine components that were dissolved into the spray solution were changed from 1:0.25 to 1:2.5. The phosphor particles prepared from the spray solution with the proper amount of ammonium chloride added to the spray solution had fine sizes and regular morphologies. The phase-pure Ca 8Mg(SiO 4) 4Cl 2:Eu 2+ phosphor particles were obtained from the spray solution that had a ratio of calcium to chlorine components in the range of 1:0.5 to 1:1.5. The post-treated phosphor particles had a broad excitation wavelength that ranged from 260 to 480 nm, irrespective of the amount of ammonium chloride added to the spray solution. The phosphor particles prepared from the spray solution with a 1:1 ratio of calcium to chlorine had maximum emission intensity under a long-wavelength ultraviolet.

Photo-luminescent properties of Eu 3+ ion-doped Ca 4REO(BO 3) 3 (RE [dbnd]La,Y,Gd)

Europium-doped materials Ca 4REO(BO 3) 3 (RE=La,Y,Gd) were first synthesized by a sol–gel process technique. The reaction temperature of the sol–gel process was 300 °C lower than that of solid-state reaction and the reaction time of sol–gel process was shorter. The photo-luminescence characteristics of Eu-doped Ca 4REO(BO 3) 3 (RE=La,Y,Gd) indicated that all compounds exhibited strong luminescence of 5D 0– 7F 2 at 608 nm under excitation at 242 nm. The emission intensity of phosphors prepared by sol–gel process was higher than those prepared by solid-state reaction; particularly the compound Ca 4La 0.9Eu 0.1O(BO 3) 3 prepared by sol–gel process presented the highest brightness. SEM images showed that particles prepared by sol–gel process had more regular morphology and smaller grain size.

Luminescence Properties of Terbium-, Cerium-, or Europium-Doped α-Sialon Materials

New interesting luminescent α-sialon (M(m/val+)val+ Si12-(m+n) Al(m+n)OnN(16−n)) (M=Ca, Y) materials doped with Ce, Tb, or Eu have been prepared and their luminescence properties studied. These show that Tb and Ce are in the 3+ and Eu in the 2+ state. Low-energy 4f↔5d transitions are observed as compared to the luminescence of these ions doped in oxidic host-lattices. This is partially explained by the nitrogen-rich coordination of the rare-earth ion and partially by the narrow size of the lattice site. The latter gives rise to a strong crystal-field splitting of the 5d band and a rather large Stokes shift for Ce3+ and Eu2+ (6500–7500 and 7000–8000 cm−1, respectively). For (Y,Tb)-α-sialon the Tb3+ 4f→5d excitation band (∼260 nm) is in the low-energy host-lattice absorption band (⩽290 nm), giving rise to a strong absorption for 254-nm excitation, but a low quantum efficiency. The latter is due to photoionization processes or selective excitation of Tb3+ at the defect-rich surface, resulting in radiationless transitions. Ce- and Eu-doped Ca–α-sialon show bright long-wavelength luminescence (maxima at 515–540 and 560–580 nm for Ce and Eu, respectively) with a high quantum efficiency and high absorption for 365- and 254-nm excitation. The Eu2+ emission intensity and absorption increases for increasing m, which is explained by the Eu2+ richer α-sialon composition. The position of the Eu2α emission does not shift with changing composition of the host-lattice (m, n values), indicating that the local coordination of the Eu2+ ion is hardly dependent on the matrix composition.